With the increasing development of network technologies, a broad-bandwidth network transmission method is widely used to transmit image data via network. In addition, some network products such as web camera and web digital cameras are widely used for processing digital images.
In a conventional network transmission system as shown in FIG. 1(a), an image frame captured by an image sensor 11 is transmitted to an image processor 12 for image processing. The processed image data are temporarily stored in a buffer memory 13 disposed inside or outside the image processor 12 or directly outputted to a computer 14.
Referring to FIG. 1(b), a timing waveform diagram of the related signals processed in the network transmission system is shown as an example. The overall time period required to process an image frame F is defined as an image frame processing period and includes an exposure period t1, an image data outputting period t2 and an idle period t3. Generally, the image frame processing period is a reciprocal of the maximum number of image frames outputted by the image sensor 11 per second. In response to an initial signal, the image frame F begins to be transmitted to the image processor 12. After the very short exposure period t1, six image data segments D1˜D6 consisting the image frame F are sequentially outputted to the image processor 12 within the image data outputting period t2. Meanwhile, these image data segments D1˜D6 are outputted to the image processor 12 to be processed within an image data processing period tp0, which is equal to the image data outputting period t2. After the idle period t3, another image frame can be exposed and then outputted from the image sensor 11 to the image processor 12 to be processed in a similar manner.
The image processor 12 is for example a digital signal processor. The image sensor 11 can be a CMOS (complementary metal-oxide semiconductor) image sensor or a CCD (charge-coupled device) image sensor. Conventionally, for achieving real-time data transmission and saving cost, no extra flow control strategy such as FIFO (first in, first out) is given to the image sensor 11. In the case that a previous image frame received from the image sensor 11 has not completed image processing by the image processor 12 while a new image frame is coming, a problem in data overrun may occur. For example, if the second image data D2 is still being processed by the image processor 12, the immediately following third image data D3 entering the image processor 12 may overlay the second image data D2. Such data overrun may lead to a succession of transmission errors occurring in the subsequently received image data D4˜D6.